Severe neuromuscular forms of glycogen storage disease type IV: Histological, clinical, biochemical, and molecular findings in a large French case series

Glycogen storage disease type IV (GSD IV), also called Andersen disease, or amylopectinosis, is a highly heterogeneous autosomal recessive disorder caused by a glycogen branching enzyme (GBE, 1,4-alpha-glucan branching enzyme) deficiency secondary to pathogenic variants on GBE1 gene. The incidence is evaluated to 1:600 000 to 1:800 000 of live births. GBE deficiency leads to an excessive deposition of structurally abnormal, amylopectin-like glycogen in affected tissues (liver, skeletal muscle, heart, nervous system, etc.). Diagnosis is often guided by histological findings and confirmed by GBE activity deficiency and molecular studies. Severe neuromuscular forms of GSD IV are very rare and of disastrous prognosis. Identification and characterization of these forms are important for genetic counseling for further pregnancies. Here we describe clinical, histological, enzymatic, and molecular findings of 10 cases from 8 families, the largest case series reported so far, of severe neuromuscular forms of GSD IV along with a literature review. Main antenatal features are: fetal akinesia deformation sequence or arthrogryposis/joint contractures often associated with muscle atrophy, decreased fetal movement, cystic hygroma, and/or hydrops fetalis. If pregnancy is carried to term, the main clinical features observed at birth are severe hypotonia and/or muscle atrophy, with the need for mechanical ventilation, cardiomyopathy, retrognathism, and arthrogryposis. All our patients were stillborn or died within 1 month of life. In addition, we identified five novel GBE1 variants.

Glycogen storage disease type IV without detectable polyglucosan bodies: importance of broad gene panels

Glycogen storage disease type IV (GSD IV) is caused by mutations in the glycogen branching enzyme 1 (GBE1) gene and is characterized by accumulation of polyglucosan bodies in liver, muscle and other tissues. We report three cases with neuromuscular forms of GSD IV, none of whom had polyglucosan bodies on muscle biopsy. The first case had no neonatal problems and presented with delayed walking. The other cases presented at birth: one with arthrogryposis, hypotonia, and respiratory distress, the other with talipes and feeding problems. All developed a similar pattern of axial weakness, proximal upper limb weakness and scapular winging, and much milder proximal lower limb weakness. Our cases expand the phenotypic spectrum of neuromuscular GSD IV, highlight that congenital myopathy and limb girdle weakness can be caused by mutations in GBE1, and emphasize that GSD IV should be considered even in the absence of characteristic polyglucosan bodies on muscle biopsy.

Diagnosis and management of glycogen storage disease type IV, including adult polyglucosan body disease: A clinical practice resource

Glycogen storage disease type IV (GSD IV) is an ultra-rare autosomal recessive disorder caused by pathogenic variants in GBE1 which results in reduced or deficient glycogen branching enzyme activity. Consequently, glycogen synthesis is impaired and leads to accumulation of poorly branched glycogen known as polyglucosan. GSD IV is characterized by a remarkable degree of phenotypic heterogeneity with presentations in utero, during infancy, early childhood, adolescence, or middle to late adulthood. The clinical continuum encompasses hepatic, cardiac, muscular, and neurologic manifestations that range in severity. The adult-onset form of GSD IV, referred to as adult polyglucosan body disease (APBD), is a neurodegenerative disease characterized by neurogenic bladder, spastic paraparesis, and peripheral neuropathy. There are currently no consensus guidelines for the diagnosis and management of these patients, resulting in high rates of misdiagnosis, delayed diagnosis, and lack of standardized clinical care. To address this, a group of experts from the United States developed a set of recommendations for the diagnosis and management of all clinical phenotypes of GSD IV, including APBD, to support clinicians and caregivers who provide long-term care for individuals with GSD IV. The educational resource includes practical steps to confirm a GSD IV diagnosis and best practices for medical management, including (a) imaging of the liver, heart, skeletal muscle, brain, and spine, (b) functional and neuromusculoskeletal assessments, (c) laboratory investigations, (d) liver and heart transplantation, and (e) long-term follow-up care. Remaining knowledge gaps are detailed to emphasize areas for improvement and future research.

Efficient correction of a deleterious point mutation in primary horse fibroblasts with CRISPR-Cas9

Phenotypic selection during animal domestication has resulted in unwanted incorporation of deleterious mutations. In horses, the autosomal recessive condition known as Glycogen Branching Enzyme Deficiency (GBED) is the result of one of these deleterious mutations (102C > A), in the first exon of the GBE1 gene (GBE1102C>A). With recent advances in genome editing, this type of genetic mutation can be precisely repaired. In this study, we used the RNA-guided nuclease CRISPR-Cas9 (clustered regularly-interspaced short palindromic repeats/CRISPR-associated protein 9) to correct the GBE1102C>A mutation in a primary fibroblast cell line derived from a high genetic merit heterozygous stallion. To correct this mutation by homologous recombination (HR), we designed a series of single guide RNAs (sgRNAs) flanking the mutation and provided different single-stranded donor DNA templates. The distance between the Cas9-mediated double-stranded break (DSB) to the mutation site, rather than DSB efficiency, was the primary determinant for successful HR. This framework can be used for targeting other harmful diseases in animal populations.

Glycogen storage disease type IV: novel mutations and molecular characterization of a heterogeneous disorder

Glycogen storage disease type IV (GSD IV; Andersen disease) is caused by a deficiency of glycogen branching enzyme (GBE), leading to excessive deposition of structurally abnormal, amylopectin-like glycogen in affected tissues. The accumulated glycogen lacks multiple branch points and thus has longer outer branches and poor solubility, causing irreversible tissue and organ damage. Although classic GSD IV presents with early onset of hepatosplenomegaly with progressive liver cirrhosis, GSD IV exhibits extensive clinical heterogeneity with respect to age at onset and variability in pattern and extent of organ and tissue involvement. With the advent of cloning and determination of the genomic structure of the human GBE gene (GBE1), molecular analysis and characterization of underlying disease-causing mutations is now possible. A variety of disease-causing mutations have been identified in the GBE1 gene in GSD IV patients, many of whom presented with diverse clinical phenotypes. Detailed biochemical and genetic analyses of three unrelated patients suspected to have GSD IV are presented here. Two novel missense mutations (p.Met495Thr and p.Pro552Leu) and a novel 1-bp deletion mutation (c.1999delA) were identified. A variety of mutations in GBE1 have been previously reported, including missense and nonsense mutations, nucleotide deletions and insertions, and donor and acceptor splice-site mutations. Mutation analysis is useful in confirming the diagnosis of GSD IV--especially when higher residual GBE enzyme activity levels are seen and enzyme analysis is not definitive--and allows for further determination of potential genotype/phenotype correlations in this disease.

Branching enzyme deficiency/glycogenosis storage disease type IV presenting as a severe congenital hypotonia: muscle biopsy and autopsy findings, biochemical and molecular genetic studies

The fatal infantile neuromuscular presentation of branching enzyme deficiency (glycogen storage disease type IV) due to mutations in the gene encoding the glycogen branching enzyme, is a rare but probably underdiagnosed cause of congenital hypotonia. We report an infant girl with severe generalized hypotonia, born at 33 weeks gestation who required ventilatory assistance since birth. She had bilateral ptosis, mild knee and foot contractures and echocardiographic evidence of cardiomyopathy. A muscle biopsy at 1 month of age showed typical polyglucosan storage. The autopsy at 3.5 months of age showed frontal cortex polymicrogyria and polyglucosan bodies in neurons of basal ganglia, thalamus, substantia innominata, brain stem, and myenteric plexus, as well as liver involvement. Glycogen branching enzyme activity in muscle was virtually undetectable. Sequencing of the GBE1 gene revealed a homozygous 28 base pair deletion and a single base insertion at the same site in exon 5. This case confirms previous observations that GBE deficiency ought to be included in the differential diagnosis of congenital hypotonia and that the phenotype correlates with the 'molecular severity' of the mutation.

Neuropathological study of skeletal muscle, heart, liver, and brain in a neonatal form of glycogen storage disease type IV associated with a new mutation in GBE1 gene

Glycogen storage disease type IV (GSD IV, or Andersen disease) is an autosomal recessive disorder due to the deficiency of 1,4-alpha-glucan branching enzyme (or glycogen branching enzyme, GBE1), resulting in an accumulation of amylopectin-like polysaccharide in muscle, liver, heart and central and peripheral nervous system. Typically, the presentation is in childhood with liver involvement up to cirrhosis. The neuromuscular form varies in onset (congenital, perinatal, juvenile and adult) and in severity. Congenital cases are rare, and fewer than 20 cases have been described and genetically determined so far. This form is characterized by polyhydramnios, neonatal hypotonia, and neuronal involvement; hepatopathy is uncommon, and the babies usually die between 4 weeks and 4 months of age. We report the case of an infant who presented severe hypotonia, dilatative cardiomyopathy, mild hepatopathy, and brain lateral ventricle haemorrhage, features consistent with the congenital form of GSD IV. He died at one month of life of cardiorespiratory failure. Muscle biopsy and heart and liver autoptic specimens showed many vacuoles filled with PAS-positive diastase-resistant materials. Electron-microscopic analysis showed mainly polyglucosan accumulations in all the tissues examined. Postmortem examination showed the presence of vacuolated neurons containing this abnormal polysaccharide. GBE1 biochemical activity was virtually absent in muscle and fibroblasts, and totally lacking in liver and heart as well as glycogen synthase activity. GBE1 gene sequence analysis revealed a novel homozygous nonsense mutation, p.E152X, in exon 4, correlating with the lack of enzyme activity and with the severe neonatal involvement. Our findings contribute to increasing the spectrum of mutation associated with congenital GSD IV.

Non-lethal congenital hypotonia due to glycogen storage disease type IV

Glycogen storage disease type IV (GSD-IV) is an autosomal recessive genetic disorder due to a deficiency in the activity of the glycogen branching enzyme (GBE). A deficiency in GBE activity results in the accumulation of glycogen with fewer branching points and long, unbranched outer chains. The disorder results in a variable phenotype, including musculoskeletal, cardiac, neurological, and hepatic involvement, alone or in continuum, which can be identified at any stage of life. The classic form of GSD-IV is a hepatic presentation, which presents in the first 18 months of life with failure to thrive, hepatomegaly, and cirrhosis that progresses to liver failure, resulting in death by age 5 years. A severe congenital musculoskeletal phenotype with death in the neonatal period has also been described. We report an unusual case of congenital musculoskeletal presentation of GSD-IV with stable congenital hypotonia, gross motor delay, and severe fibro-fatty replacement of the musculature, but no hepatic or cardiac involvement. Molecular analysis revealed two novel missense mutations with amino acid changes in the GBE gene (Q236H and R262C), which may account for the mild phenotype.

Multisystem involvement in a patient due to accumulation of amylopectin-like material with diminished branching enzyme activity

We report a 13-year-old boy with multisystem involvement secondary to accumulation of amylopectin-like material. He was born to consanguineous parents at full term without any complications and his maternal perinatal history was uneventful. His parents were cousins. He had normal growth and development except for his weight. His sister died from an unexplained cardiomyopathy at the age of 8 years. Our patient's initial symptom was severe heart failure. Since he also had a complaint of muscle weakness, electromyography was performed which showed muscle involvement. The diagnosis was suggested by tissue biopsy of skeletal muscle showing intracellular, basophilic, diastase-resistant, periodic acid-Schiff-positive inclusion bodies and was confirmed by the presence of a completed branching enzyme deficiency. Similar intracytoplasmic inclusion-like bodies were also found in liver biopsy, but very few in number compared with the skeletal muscle. The patient died from an intercurrent infection. Postmortem endomyocardial biopsy revealed the same intracytoplasmic inclusions as described above affecting almost all myocardial cells. Ultrastructural examination of liver biopsy was nondiagnostic; however, myocardium showed prominent, large, intracytoplasmic deposits. Glycogen branching enzyme gene sequence was normal, and thus classical branching enzyme deficiency was excluded. Our patient represents the first molecular study performed on a patient in whom there was multiple system involvement secondary to accumulation of amylopectin-like material. We suggest that this is an as yet undefined and different phenotype of glycogen storage disease associated with multisystemic involvement.

Congenital type IV glycogenosis: the spectrum of pleomorphic polyglucosan bodies in muscle, nerve, and spinal cord with two novel mutations in the GBE1 gene

A diagnosis of GSD-IV was established in three premature, floppy infants based on characteristic, however unusually pleomorphic polyglucosan bodies at the electron microscopic level, glycogen branching enzyme deficiency in two cases, and the identification of GBE1 mutations in two cases. Pleomorphic polyglucosan bodies in muscle fibers and macrophages, and less severe in Schwann cells and microglial cells were noted. Most of the inclusions were granular and membrane-bound; others had an irregular contour, were more electron dense and were not membrane bound, or homogenous ('hyaline'). A paracrystalline pattern of granules was repeatedly noted showing a periodicity of about 10 nm with an angle of about 60 degrees or 120 degrees at sites of changing linear orientation. Malteser crosses were noted under polarized light in the larger inclusions. Some inclusions were PAS positive and others were not. Severely atrophic muscle fibers without inclusions, but with depletion of myofibrils in the plane of section studied indicated the devastating myopathic nature of the disease. Schwann cells and peripheral axons were less severely affected as was the spinal cord. Two novel protein-truncating mutations (c.1077insT, p.V359fsX16; g.101517_127067del25550insCAGTACTAA, DelExon4-7) were identified in these families. The present findings extend previous studies indicating that truncating GBE1 mutations cause a spectrum of severe diseases ranging from generalized intrauterine hydrops to fatal perinatal hypotonia and fatal cardiomyopathy in the first months of life.

Unclassified polysaccharidosis of the heart and skeletal muscle in siblings

We describe a 15-year-old boy and his 19-year-old sister with progressive dilated cardiomyopathy and mild non-progressive proximal lower limb myopathy, secondary to the accumulation of amylopectin-like fibrillar glycogen, (polyglucosan) bodies, in heart and skeletal muscle. Evidence of idiopathic amylopectinosis or polysaccharidosis was demonstrated in heart and skeletal muscle tissue by histology, electron microscopy, biochemical, and genetic analysis. In both siblings the heart muscle stored PAS-positive, proteinase-k resistant and partly diastase resistant granulo-filamentous material, simulating polyglucosan bodies. Glycogen branching enzyme activity, and phosphofructokinase enzyme activity, measured in skeletal muscle tissue and explanted heart tissue were all within the normal limits, however glycogen content was elevated. Furthermore, GBE1, PRKAG2, desmin, alphabeta-crystallin, ZASP, myotilin, and LAMP-2 gene sequencing revealed no mutation, excluding e.g. glycogen storage disease type 4 and desmin-related myofibrillar cardiomyopathies. In both patients the diagnosis of an idiopathic polysaccharidosis with progressive dilated cardiomyopathy was made, requiring heart transplantation at age 13 and 14, respectively. Both patients belong to an autosomal recessive group of biochemically and genetically unclassified severe vacuolar glycogen storage disease of the heart and skeletal muscle. Up to now unidentified glycogen synthesis or glycogen degradation pathways are supposed to contribute to this idiopathic glycogen storage disease.

Primary periodic paralyses

OBJECTIVE

To review the current knowledge about primary periodic paralyses (PPs).

RESULTS

Periodic paralyses are a heterogeneous group of disorders, clinically characterized by episodes of flaccid muscle weakness, occurring at irregular intervals. PPs are divided into primary (hereditary) and secondary (acquired) forms of which the secondary PPs are much more common than the primary PPs. Primary PPs are due to mutations in genes encoding for subunits of channel proteins of the skeletal muscle membrane, such as the muscular sodium, potassium or calcium channels, or the SCL4A1 protein. Primary PPs include entities such as hyperkalemic PP, hypokalemic PP, paramyotonia congenita von Eulenburg, Andersen's syndrome, thyrotoxic PP, distal renal tubular acidosis, X-linked episodic muscle weakness syndrome and congenital myasthenic syndromes. Attacks of weakness or myotonia may be triggered or enhanced by vigorous exercise, cold, potassium-rich food, emotional stress, drugs such as glucocorticosteroids, insulin or diuretics, or pregnancy. Depending on the pathomechanism, episodes of weakness may respond to mild exercise, ingestion of potassium, carbohydrates, salbutamol, calcium gluconate, thiazide diuretics, carboanhydrase inhibitors, such as acetazolamide or dichlorphenamine, and episodes may be prevented by avoidance of potassium-rich food, or drugs, which increase serum potassium.

CONCLUSION

This review presents and discusses current knowledge and recent advances in the etiology, molecular genetics, genotype-phenotype correlations, pathogenesis, diagnosis and treatment of primary PPs.

High frequency of missense mutations in glycogen storage disease type VI

Deficiency of liver glycogen phosphorylase in glycogen storage disease (GSD) type VI results in a reduced ability to mobilize glucose from glycogen. Six mutations of the PYGL gene, which encodes the liver isoform of the enzyme, have been identified in the literature. We have characterized eight patients from seven families with GSD type VI and identified 11 novel PYGL gene defects. The majority of the mutations were missense, resulting in the substitution of highly conserved residues. These could be grouped into those that were predicted to affect substrate binding (p.V456M, p.E673K, p.S675L, p.S675T), pyridoxal phosphate binding (p.R491C, p.K681T), or activation of glycogen phosphorylase (p.Q13P) or that had an unknown effect (p.N632I and p.D634H). Two mutations were predicted to result in null alleles, p.R399X and [c.1964_1969inv6;c.1969+1_+4delGTAC]. Only 7 of the 23 (30%) reported PYGL alleles carry nonsense, splice site or frameshift mutations compared to 68-80% of affected alleles of the highly homologous muscle glycogen phosphorylase gene, PYGM, that underlie McArdle disease. There was heterogeneity in the clinical symptoms observed in affected individuals. These varied from hepatomegaly and subclinical hypoglycaemia, to severe hepatomegaly with recurrent severe hypoglycaemia and postprandial lactic acidosis. We conclude that deficiency of liver glycogen phosphorylase is predominantly the result of missense mutations affecting enzyme activity. There are no common mutations and the severity of clinical symptoms varies significantly.

Null mutations and lethal congenital form of glycogen storage disease type IV

Glycogen branching enzyme deficiency (glycogen storage disease type IV, GSD-IV) is a rare autosomal recessive disorder of the glycogen synthesis with high mortality. Two female newborns showed severe hypotonia at birth and both died of cardiorespiratory failure, at 4 and 12 weeks, respectively. In both patients, muscle biopsies showed deposits of PAS-positive diastase-resistant material and biochemical analysis in cultured fibroblasts showed markedly reduced glycogen branching enzyme activity. Direct sequencing of GBE1 gene revealed that patient 1 was homozygous for a novel c.691+5 g>c in intron 5 (IVS5+5 g>c). RT-PCR analysis of GBE1 transcripts from fibroblasts cDNA showed that this mutation produce aberrant splicing. Patient 2 was homozygous for a novel c.1643G>A mutation leading to a stop at codon 548 in exon 13 (p.W548X). These data underscore that in GSD-IV a severe phenotype correlates with null mutations, and indicate that RNA analysis is necessary to characterize functional consequences of intronic mutations.

Neuromuscular forms of glycogen branching enzyme deficiency

Deficiency of glycogen branching enzyme is causative of Glycogen Storage Disease type IV (GSD-IV), a rare autosomal recessive disorder of the glycogen synthesis, characterized by the accumulation of amylopectin-like polysaccharide, also known as polyglucosan, in almost all tissues. Its clinical presentation is variable and involves the liver or the neuromuscular system and different mutations in the GBE1 gene, located on chromosome 3, have been identified in both phenotypes. This review will addresses the neuromuscular clinical variants, focusing on the molecular genetics aspects of this disorder.

A complex rearrangement in GBE1 causes both perinatal hypoglycemic collapse and late-juvenile-onset neuromuscular degeneration in glycogen storage disease type IV of Norwegian forest cats

Deficiency of glycogen branching enzyme (GBE) activity causes glycogen storage disease type IV (GSD IV), an autosomal recessive error of metabolism. Abnormal glycogen accumulates in myocytes, hepatocytes, and neurons, causing variably progressive, benign to lethal organ dysfunctions. A naturally occurring orthologue of human GSD IV was described previously in Norwegian forest cats (NFC). Here, we report that while most affected kittens die at or soon after birth, presumably due to hypoglycemia, survivors of the perinatal period appear clinically normal until onset of progressive neuromuscular degeneration at 5 months of age. Molecular investigation of affected cats revealed abnormally spliced GBE1 mRNA products and lack of GBE cross-reactive material in liver and muscle. Affected cats are homozygous for a complex rearrangement of genomic DNA in GBE1, constituted by a 334 bp insertion at the site of a 6.2 kb deletion that extends from intron 11 to intron 12 (g. IVS11+1552_IVS12-1339 del6.2kb ins334 bp), removing exon 12. An allele-specific, PCR-based test demonstrates that the rearrangement segregates with the disease in the GSD IV kindred and is not found in unrelated normal cats. Screening of 402 privately owned NFC revealed 58 carriers and 4 affected cats. The molecular characterization of feline GSD IV will enhance further studies of GSD IV pathophysiology and development of novel therapies in this unique animal model.

Spätmanifestation einer Polyglykosankörpermyopathie

We report two patients with polyglycosan body disease manifesting in adulthood. Clinical, electrophysiological, and histopathological characteristics of their disorders are summarized, and diagnostic classification is discussed.

Allele frequency and likely impact of the glycogen branching enzyme deficiency gene in Quarter Horse and Paint Horse populations

Glycogen Branching Enzyme Deficiency (GBED), a fatal condition recently identified in fetuses and neonatal foals of the Quarter Horse and Paint Horse lineages, is caused by a nonsense mutation in codon 34 of the GBE1 gene, which prevents the synthesis of a functional GBE protein and severely disrupts glycogen metabolism. The aims of this project were to determine the mutant GBE1 allele frequency in random samples from the major relevant horse breeds, as well as the frequency with which GBED is associated with abortion and early neonatal death using the tissue archives from veterinary diagnostic laboratories. The mutant GBE1 allele frequency in registered Quarter Horse, Paint Horse, and Thoroughbred populations was 0.041, 0.036, and 0.000, respectively. Approximately 2.5% of fetal and early neonatal deaths in Quarter Horse-related breeds submitted to 2 different US diagnostic laboratories were homozygous for the mutant GBE1 allele, with the majority of these being abortions. Retrospective histopathology of the homozygotes detected periodic acid Schiff's (PAS)-positive inclusions in the cardiac or skeletal muscle, which is characteristic of GBED, in 8 out of the 9 cases. Pedigree and genotype analyses supported the hypothesis that GBED is inherited as a simple recessive trait from a single founder. The frequency with which GBED is associated with abortion and neonatal mortality in Quarter Horse-related breeds makes the DNA-based test valuable in determining specific diagnoses and designing matings that avoid conception of a GBED foal.

Fetal type IV glycogen storage disease: clinical, enzymatic, and genetic data of a pure muscular form with variable and early antenatal manifestations in the same family

We report on a family of three consecutive fetuses affected by type IV glycogen storage disease (GSD IV). In all cases, cervical cystic hygroma was observed on the 12-week-ultrasound examination. During the second trimester, fetal hydrops developed in the first pregnancy whereas fetal akinesia appeared in the second pregnancy. The diagnosis was suggested by microscopic examination of fetal tissues showing characteristic inclusions exclusively in striated fibers, then confirmed by enzymatic studies on frozen muscle. Antenatal diagnosis was performed on the third and fourth pregnancies: cervical cystic hygroma and low glycogen branching enzyme (GBE) activity on chorionic villi sample (CVS) were detected in the third pregnancy whereas ultrasound findings were normal and GBE activity within normal range on CVS in the fourth pregnancy. Molecular analysis showed that the mother was heterozygous for a c.1471G > C mutation in exon 12, leading to the replacement of an alanine by a tyrosine at codon 491 (p.A491T); the father was heterozygous for a c.895G > T mutation in exon 7, leading to the creation of a stop codon at position 299 (p.G299X). GSD IV has to be considered in a context of cervical cystic hygroma with normal karyotype, particularly when second trimester hydrops or akinesia develop. Enzymatic analysis of GBE must be performed on CVS or amniotic cells to confirm the diagnosis. Characteristic intracellular inclusions are specific to the disease and should be recognized, even in macerated tissues after fetal death. Genetic analysis of the GBE gene may help to shed some light on the puzzling diversity of GSD IV phenotypes.

Prenatal diagnosis of glycogen storage disease type IV

BACKGROUND

Glycogen storage disease type IV (GSD-IV) is a rare autosomal recessive disorder due to mutations in the GBE1 gene causing deficiency of the glycogen branching enzyme (GBE). Prenatal diagnosis has occasionally been performed by the measurement of the GBE activity in cultured chorionic villi (CV) cells.

METHODS

Two unrelated probands with severe hypotonia at birth and death during the neonatal period were diagnosed with GSD-IV on the basis of postmortem histological findings. DNA analysis revealed truncating GBE1 mutations in both families.

RESULTS

Prenatal diagnosis was performed in subsequent pregnancies by determination of branching enzyme activity and DNA analysis of CV or cultured amniocytes. Detailed autopsies of the affected fetuses at 14 and 24 weeks of gestation demonstrated intracellular inclusions of abnormal glycogen characteristic of GSD-IV.

CONCLUSION

Prenatal diagnosis of GSD-IV by DNA analysis is highly accurate in genetically confirmed cases.

Clinical and genetic heterogeneity of branching enzyme deficiency (glycogenosis type IV)

BACKGROUND

Glycogen storage disease type IV (GSD-IV) is a clinically heterogeneous autosomal recessive disorder due to glycogen branching enzyme (GBE) deficiency and resulting in the accumulation of an amylopectin-like polysaccharide. The typical presentation is liver disease of childhood, progressing to lethal cirrhosis. The neuromuscular form of GSD-IV varies in onset (perinatal, congenital, juvenile, or adult) and severity.

OBJECTIVE

To identify the molecular bases of different neuromuscular forms of GSD-IV and to establish possible genotype/phenotype correlations.

METHODS

Eight patients with GBE deficiency had different neuromuscular presentations: three had fetal akinesia deformation sequence (FADS), three had congenital myopathy, one had juvenile myopathy, and one had combined myopathic and hepatic features. In all patients, the promoter and the entire coding region of the GBE gene at the RNA and genomic level were sequenced.

RESULTS

Nine novel mutations were identified, including nonsense, missense, deletion, insertion, and splice-junction mutations. The three cases with FADS were homozygous, whereas all other cases were compound heterozygotes.

CONCLUSIONS

This study expands the spectrum of mutations in the GBE gene and confirms that the neuromuscular presentation of GSD-IV is clinically and genetically heterogeneous.

Amylopectinosis disease isolated to the heart with normal glycogen branching enzyme activity and gene sequence

We report a 17-month-old female patient with a rare cause of cardiomyopathy secondary to accumulation of amylopectin-like material (fibrillar glycogen) isolated to the heart. Evidence of amylopectinosis isolated to cardiac myocytes in this patient was demonstrated by histology and electron microscopy. Glycogen content, glycogen branching enzyme (GBE) activity, as well as phosphofructokinase enzyme activities measured in liver, skeletal muscle, fibroblasts and ex-transplanted heart tissue were all in the normal to lower normal ranges. Normal skeletal muscle and liver tissue histology and GBE activity, normal GBE activity in skin fibroblasts, plus normal GBE gene sequence in this patient exclude the classical branching enzyme deficiency (type IV GSD). We believe that this is an as yet uncharacterized and novel phenotype of GSD associated with cardiomyopathy, in which there is an imbalance in the regulation of glycogen metabolism limited to the heart.

Andersen syndrome: the newest variant of the hereditary-familial long QT syndrome

Andersen's Syndrome is a rare disease, hereditary with autosomal dominant transmission, of the ion channels of the sarcolemmal membranes of the cardiac and skeletal muscles (channelopathy), which affects chromosome 17 of the KCNJ2 gene, responsible for encoding the outward potassium delayed rectifier current KIR2.1, resulting in a loss or suppression of the function of this channel.

Neonatal type IV glycogen storage disease associated with "null" mutations in glycogen branching enzyme 1

The fatal neonatal form of type IV glycogen storage disease (GSD IV) was diagnosed on light and electron microscopy and by analysis of GBE1 , the gene encoding glycogen branching enzyme. We report two novel truncating mutations, as well as the first genomic mutational analysis of GBE1 using denaturing high performance liquid chromatography.

Glycogen branching enzyme (GBE1) mutation causing equine glycogen storage disease IV

Comparative biochemical and histopathological evidence suggests that a deficiency in the glycogen branching enzyme, encoded by the GBE1 gene, is responsible for a recently identified recessive fatal fetal and neonatal glycogen storage disease (GSD) in American Quarter Horses termed GSD IV. We have now derived the complete GBE1 cDNA sequences for control horses and affected foals, and identified a C to A substitution at base 102 that results in a tyrosine (Y) to stop (X) mutation in codon 34 of exon 1. All 11 affected foals were homozygous for the X34 allele, their 11 available dams and sires were heterozygous, and all 16 control horses were homozygous for the Y34 allele. The previous findings of poorly branched glycogen, abnormal polysaccharide accumulation, lack of measurable GBE1 enzyme activity and immunodetectable GBE1 protein, coupled with the present observation of abundant GBE1 mRNA in affected foals, are all consistent with the nonsense mutation in the 699 amino acid GBE1 protein. The affected foal pedigrees have a common ancestor and contain prolific stallions that are likely carriers of the recessive X34 allele. Defining the molecular basis of equine GSD IV will allow for accurate DNA testing and the ability to prevent occurrence of this devastating disease affecting American Quarter Horses and related breeds.

Le syndrome d’Andersen : une forme particulière de paralysie périodique avec dysrythmie cardiaque

Andersen syndrome includes a clinical triad with periodic paralysis, cardiac arrhythmia and dysmorphic features most often mild but relevant. It is a potassium channelopathy due to mutation of KCJN2 gene coding for Kir 2.1 protein. We report a familial case with mutation R218W of Kir 2.1 and discuss the main phenotypic and genetic aspects of Andersen syndrome. Muscle manifestations are essentially a periodic paralysis most often of hypokaliemic type. Muscle biopsy reveals tubular aggregates but can be normal as it is shown in the same patient in our kindred. Our proband complained of paralytic attacks since childhood and at adult age she demonstrated a mild permanent deficit of pelvic girdle muscles as it has been described in other types of periodic paralysis after a long duration course. Cardiac manifestations may include in a variable manner a long QT syndrome, premature ventricular contractions, complex ventricular ectopy, polymorphic or bidirectional ventricular tachycardia. Imipramine had a positive effect on arrhythmia in our case. Dysmorphic features are often mild and have to be cautiously looked for as a clue to the diagnosis of Andersen syndrome. They can be easily overlooked if not systematically looked for. Clinical expressivity is variable including in the same family. In our observation, the daughter showed a complete triad, early expressed, which allowed the diagnosis. Her father was late diagnosed on ventricular dysrhytmia but without muscle manifestations and dysmorphic features. Since KCJN2 gene mutation identification, locus heterogeneity of Andersen syndrome was shown. Andersen syndrome kindreds without mutations in KCNJ2 were clinically indistinguishable from KCNJ2-associated subjects. KCNJ2 gene encodes the inward rectifier K+ channel Kir2.1 which plays an important role in maintaining membrane potential and during the terminal phase of cardiac action potential repolarization. Several studies showed a dominant negative effect of the mutation on Kir 2.1 channel function.

Fatal infantile neuromuscular presentation of glycogen storage disease type IV

Glycogen storage disease type IV or Andersen disease is an autosomal recessive disorder due to deficiency of glycogen branching enzyme. Typically, glycogen storage disease type IV presents with rapidly progressive liver cirrhosis and death in childhood. Variants include a cardiopathic form of childhood, a relatively benign myopathic form of young adults, and a late-onset neurodegenerative disorder (adult polyglucosan body disease). A severe neuromuscular variant resembling Werdnig-Hoffmann disease has also been described in two patients. The objective was to describe two additional infants with the neuromuscular variant and novel mutations in the GBE1 gene. Branching enzyme assay, Western blot, RT-PCR and sequencing were performed in muscle biopsies from both patients. The cDNA of patient 1 was subcloned and sequenced to define the mutations. Muscle biopsies showed accumulation of periodic acid Schiff-positive, diastase-resistant storage material in both patients and increased lysosomal enzyme activity in patient 1. Branching enzyme activity in muscle was negligible in both patients, and Western blot showed decreased branching enzyme protein. Patient 1 had two single base pair deletions, one in exon 10 (1238delT) and the other in exon 12 (1467delC), and each parent was heterozygous for one of the deletions. Patient 2 had a large homozygous deletion that spanned 627 bp and included exons 8-12. Patient 1, who died at 41 days, had neurophysiological and neuropathological features of Spinal Muscular Atrophy. Patient 2, who died at 5(1/2) weeks, had a predominantly myopathic process. The infantile neuromuscular form of glycogen storage disease type IV is considered extremely rare, but our encountering two patients in close succession suggests that the disease may be underdiagnosed.

The intracellular transport of chylomicrons requires the small GTPase, Sar1b

PURPOSE OF REVIEW

The transport of lipoproteins through the secretory pathways of enterocytes and hepatocytes is pivotal for whole-body lipid homeostasis. This review focuses on the assembly and structural evolution of COPII (coat protein) transport carriers that are essential for the transport of chylomicrons from the endoplasmic reticulum to the Golgi apparatus.

RECENT FINDINGS

The assembly of endoplasmic reticulum to Golgi transport carriers commences with the coating of specific areas of the endoplasmic reticulum membrane with Sar1-GTP and the Sec23/24 heterodimer. An important advance has been the crystallographic analysis of the Sar1-Sec23/24 complex. The proteins form a bow-tie shaped structure, with a concave face that seems to match the curvature of transport carriers. Mammalian cells produce two isoforms of Sar1, designated Sar1a and Sar1b, both of which are expressed in enterocytes. Sar1b is defective in chylomicron retention disease and Anderson disease, two rare recessive disorders characterized by severe fat malabsorption and a failure to thrive in infancy. Patients with chylomicron retention disease and Anderson disease selectively retain chylomicron-like particles within membrane-bound compartments. By analogy with procollagen, chylomicrons may drive the formation of endoplasmic reticulum to Golgi transport carriers from endoplasmic reticulum sites close to, but separate from, domains of the endoplasmic reticulum coated with Sar1-Sec23/24. The COPII machinery also mediates the transport of VLDL to the Golgi.

SUMMARY

New insights into the role of the COPII machinery in the intracellular transport of cargo, including chylomicrons and VLDL, may suggest new drug targets for ameliorating the lipid abnormalities of the metabolic syndrome.

Genetic mapping of GBE1 and its association with glycogen storage disease IV in American Quarter horses

Comparative biochemical and histopathological data suggest that a deficiency in the glycogen branching enzyme (GBE) is responsible for a fatal neonatal disease in Quarter Horse foals that closely resembles human glycogen storage disease type IV (GSD IV). Identification of DNA markers closely linked to the equine GBE1 gene would assist us in determining whether a mutation in this gene leads to the GSD IV-like condition. FISH using BAC clones as probes assigned the equine GBE1 gene to a marker deficient region of ECA26q12-->q13. Four other genes, ROBO2, ROBO1, POU1F1, and HTR1F, that flank GBE1 within a 10-Mb segment of HSA3p12-->p11, were tightly linked to equine GBE1 when analyzed on the Texas A&M University 5000 rad equine radiation hybrid panel, while the GLB1, MITF, RYBP, and PROS1 genes that flank this 10-Mb interval were not linked with markers in the GBE1 group. A polymorphic microsatellite (GBEms1) in a GBE1 BAC clone was then identified and genetically mapped to ECA26 on the Animal Health Trust full-sibling equine reference family. All Quarter Horse foals affected with GSD IV were homozygous for an allele of GBEms1, as well as an allele of the most closely linked microsatellite marker, while a control horse population showed significant allelic variation with these markers. This data provides strong molecular genetic support for the candidacy of the GBE1 locus in equine GSD IV.

The genes and proteins of atherogenic lipoprotein production

Dietary fat provides a major source of nutrition, but may in excess lead to obesity, insulin resistance, high blood cholesterol levels and atherosclerosis. Here we report molecular events that co-ordinate whole-body lipid homoeostasis from insects to humans, viewed in the context of rare and common genetic disorders of apolipoprotein B-containing lipoprotein production.

Severe neonatal onset of glycogenosis type IV: clinical and laboratory findings leading to diagnosis in two siblings

Glycogenosis type IV is an autosomal recessive disease, exceptionally diagnosed at birth: only very few reports of the fatal perinatal neuromuscular form have been described. We report on two sibling male newborns who died at 10 and 4 weeks of age with clinical signs of a systemic storage disease. Prenatal history included polyhydramnios, reduced fetal movements and fetal hydrops, and Caesarean section was performed at 36 weeks of gestational age because of fetal distress. At birth, both babies showed severe hypotonia, hyporeflexia and no spontaneous breathing activity. They never showed active movements, sucking and swallowing and were respirator-dependent until death. A muscle biopsy revealed, in both patients, the presence of PAS-positive and partially diastase-resistant cytoplasmic inclusions containing granular and filamentous amylopectin-like material. This suggested that the stored material consisted of abnormal glycogen. At autopsy, ultrastructural examination of cardiac and skeletal muscle, liver, kidney and brain showed PAS-positive diastase-resistant eosinophilic cytoplasmic inclusions. Determination of branching enzyme activity, in cultured fibroblasts from the second patient, showed markedly reduced enzyme activity, confirming diagnosis of glycogenosis type IV. Our patients showed the full spectrum of both prenatal signs (hydrops, polyhydramnios) and postnatal signs (hypotonia, hyporeflexia, absence of active movements, cardiomegaly), which have been reported previously. They suffered from a very severe form of glycogenosis type IV with clinical and histological involvement of many tissues and organs. Diagnosis was accomplished on the second baby and required several biochemical and histological studies, in order to rule out both neuromuscular disorders and the most common storage diseases with neonatal onset. In our experience, the correct interpretation of the histological findings was essential in the search for the diagnosis.

A neonatal form of glycogen storage disease type IV

We report of an infant with neonatal glycogen storage disease type IV (GSD IV) who was examined for severe hypotonia and cardiomyopathy. On the muscle biopsy there were many fibers with diastase-resistant polyglucosan bodies. Glycogen branching enzyme (GBE1) activity in the muscle was markedly reduced. The infant had a homozygous single nucleotide deletion in the open reading frame of GBE1 gene.

Andersen mutations of KCNJ2 suppress the native inward rectifier current IK1 in a dominant-negative fashion

OBJECTIVE

The Andersen's syndrome is a hereditary disease, which is characterized by cardiac arrhythmias, periodic paralysis and dysmorphic features. Recently, mutations of the KCNJ2 gene, which encodes the inward rectifying potassium channel subunit Kir2.1, have been identified in affected individuals. However, the functional effects of these mutations have not yet been fully elucidated.

METHODS AND RESULTS

To clarify this situation we generated known Andersen disease mutants of KCNJ2 which did not yield any measurable K(+) currents in CHO cells indicating that the Andersen mutants failed to form functional homomultimeric complexes. EGFP-tagged KCNJ2 wild-type and mutant channels distributed in a similar homogeneous pattern in the cell membrane suggesting that protein trafficking was not altered by the Andersen mutations but rather implicating that the mutations rendered the KCNJ2 channel non-functional. In heterologous coexpression experiments the Andersen mutants exerted a dominant-negative effect on wild-type KCNJ2. However, the extent of suppression varied between the different KCNJ2 mutants. Given our results in CHO cells, we expressed the disease mutant KCNJ2-S136F in neonate rat cardiomyocytes using adenoviral gene transfer to test the effect of Andersen mutants on native I(K1). I(K1) density was indeed significantly reduced in KCNJ2-S136F-infected cells (n=9) compared to control cells (n=9) over a voltage range from -70 to -150 mV (P<0.05).

CONCLUSION

These results support that Kir2.x channels are a critical component of native I(K1) in neonate rat cardiomyocytes and that a dominant-negative suppression of I(K1) in native cells is the pathophysiological correlate of the Andersen's syndrome.

Mutations in a Sar1 GTPase of COPII vesicles are associated with lipid absorption disorders

Dietary fat is an important source of nutrition. Here we identify eight mutations in SARA2 that are associated with three severe disorders of fat malabsorption. The Sar1 family of proteins initiates the intracellular transport of proteins in COPII (coat protein)-coated vesicles. Our data suggest that chylomicrons, which vastly exceed the size of typical COPII vesicles, are selectively recruited by the COPII machinery for transport through the secretory pathways of the cell.

Function, subcellular localization and assembly of a novel mutation of KCNJ2 in Andersen's syndrome

Andersen's syndrome (AS) (which is characterized by periodic paralysis, cardiac arrhythmias and dysmorphic features), a hereditary disease, and missense mutations of KCNJ2 (which encodes an inward rectifying potassium channel) have been reported recently. We performed clinical and molecular analyses of a patient with AS, and found a novel mutation (G215D) of KCNJ2. Twelve-lead electrocardiography revealed a long QT interval and frequent premature ventricular contractions, and polymorphic ventricular tachycardia was induced by programmed electrical stimulation. Use of a conventional whole-cell patch-clamp system with COS7 cells demonstrated that the G215D mutant was non-functional, and that co-expression of wild type (WT)- and mutant-KCNJ2 shows a dominant negative effect on both inward and outward currents. We performed confocal laser scanning microscopy to assess the cellular trafficking of WT- and mutant-KCNJ2 subunits tagged with yellow fluorescent protein (YFP) and cyan fluorescent protein (CFP), respectively. Tagging with the YFP did not affect the channel function of WT-KCNJ2 and both proteins showed similar plasma membrane fluorescence patterns. Furthermore, the result of fluorescence resonance energy transfer (FRET) studies at the plasma membrane region suggested that both YFP-tagged WT- and CFP-tagged mutant-KCNJ2 combine to construct a hetero-multimer of the potassium channel. In conclusion, the G215D mutant of KCNJ2 is distributed normally in the plasma membrane, but exhibits a dominant-negative effect and reduces the Kir2.1 current, presumably due to hetero-multimer construction.

[Andersen syndrome, ventricular arrhythmias and channelopathy (a case report)]

INTRODUCTION

Recent advances in molecular genetic research have provided new insights into severe ventricular arrhythmias related to channelopathies.

CASE REPORT

A case of Andersen's syndrome followed during fourteen years is reported. This rare familial periodic paralysis is characterized by its association with dysmorphic features (micrognatia) and ventricular arrhythmias.

COMMENTS

Andersen's syndrome has been attributed to a mutation in the KCNJ2 gene which is involved not only in stabilizing cardiac rhythm, but also in modulating the excitability of skeletal muscle and in morphogenesis. This disease must be distinguished from hyperkalemic periodic paralysis due to a mutation in the skeletal muscle sodium channel gene (SCN4A) and from hypokalemic periodic paralysis related to dihydropyridine receptor mutation (CACNL1A3). Furthermore, it may not be confused with others rhythmic channelopathies (long QT syndromes, catecholaminergic polymorphic ventricular tachycardia and Brugada's syndrome).

An expanding view for the molecular basis of familial periodic paralysis

The periodic paralyses are rare disorders of skeletal muscle characterized by episodic attacks of weakness due to intermittent failure of electrical excitability. Familial forms of periodic paralysis are all caused by mutations in genes coding for voltage-gated ion channels. New discoveries in the past 2 years have broadened our views on the diversity of phenotypes produced by mutations of a single channel gene and have led to the identification of potassium channel mutations, in addition to those previously found in sodium and calcium channels. This review focuses on the clinical features, molecular genetic defects, and pathophysiologic mechanisms that underlie familial periodic paralysis.

Alterations in conserved Kir channel-PIP2 interactions underlie channelopathies

Inwardly rectifying K(+) (Kir) channels are important regulators of resting membrane potential and cell excitability. The activity of Kir channels is critically dependent on the integrity of channel interactions with phosphatidylinositol 4,5-bisphosphate (PIP(2)). Here we identify and characterize channel-PIP(2) interactions that are conserved among Kir family members. We find basic residues that interact with PIP(2), two of which have been associated with Andersen's and Bartter's syndromes. We show that several naturally occurring mutants decrease channel-PIP(2) interactions, leading to disease.

Myophosphorylase deficiency (glycogenosis type V; McArdle disease)

McArdle disease, one of the most common metabolic causes of exercise intolerance and recurrent myoglobinuria, is due to biochemical defects of the muscle isoform of glycogen phosphorylase. The gene for myophosphorylase (PGYM) is on chromosome 11, and 33 distinct mutations have been identified in patients from all over the world. In Caucasians, a nonsense mutation in exon 1 (R49X) is common enough to warrant screening of genomic DNA from blood before considering muscle biopsy. Other mutations are prevalent in different ethnic groups or are "private". Mutations are spread throughout the gene and there is no clear genotype:phenotype correlation. High-protein diet and aerobic exercise are beneficial, and gene therapy appears promising.

The variable presentations of glycogen storage disease type IV: a review of clinical, enzymatic and molecular studies

Glycogen storage disease type IV (GSD-IV), also known as Andersen disease or amylopectinosis (MIM 23250), is a rare autosomal recessive disorder caused by a deficiency of glycogen branching enzyme (GBE) leading to the accumulation of amylopectin-like structures in affected tissues. The disease is extremely heterogeneous in terms of tissue involvement, age of onset and clinical manifestations. The human GBE cDNA is approximately 3-kb in length and encodes a 702-amino acid protein. The GBE amino acid sequence shows a high degree of conservation throughout species. The human GBE gene is located on chromosome 3p14 and consists of 16 exons spanning at least 118 kb of chromosomal DNA. Clinically the classic Andersen disease is a rapidly progressive disorder leading to terminal liver failure unless liver transplantation is performed. Several mutations have been reported in the GBE gene in patients with classic phenotype. Mutations in the GBE gene have also been identified in patients with the milder non-progressive hepatic form of the disease. Several other variants of GSD-IV have been reported: a variant with multi-system involvement including skeletal and cardiac muscle, nerve and liver; a juvenile polysaccharidosis with multi-system involvement but normal GBE activity; and the fatal neonatal neuromuscular form associated with a splice site mutation in the GBE gene. Other presentations include cardiomyopathy, arthrogryposis and even hydrops fetalis. Polyglucosan body disease, characterized by widespread upper and lower motor neuron lesions, can present with or without GBE deficiency indicating that different biochemical defects could result in an identical phenotype. It is evident that this disease exists in multiple forms with enzymatic and molecular heterogeneity unparalleled in the other types of glycogen storage diseases.

Surprises of genetic engineering: a possible model of polyglucosan body disease

BACKGROUND

The authors previously reported the generation of a knockout mouse model of Pompe disease caused by the inherited deficiency of lysosomal acid alpha-glucosidase (GAA). The disorder in the knockout mice (GAA-/-) resembles the human disease closely, except that the clinical symptoms develop late relative to the lifespan of the animals. In an attempt to accelerate the course of the disease in the knockouts, the authors increased the level of cytoplasmic glycogen by overexpressing glycogen synthase (GSase) or GlutI glucose transporter.

METHODS

GAA-/- mice were crossed to transgenic mice overexpressing GSase or GlutI in skeletal muscle.

RESULTS

Both transgenics on a GAA knockout background (GS/GAA-/- and GlutI/GAA-/-) developed a severe muscle wasting disorder with an early age at onset. This finding, however, is not the major focus of the study. Unexpectedly, the mice bearing the GSase transgene, but not those bearing the GlutI transgene, accumulated structurally abnormal polysaccharide (polyglucosan) similar to that observed in patients with Lafora disease, glycogenosis type IV, and glycogenosis type VII. Ultrastructurally, the periodic acid-Schiff (PAS)-positive polysaccharide inclusions were composed of short, amorphous, irregular branching filaments indistinguishable from classic polyglucosan bodies. The authors show here that increased level of GSase in the presence of normal glycogen branching enzyme (GBE) activity leads to polyglucosan accumulation. The authors have further shown that inactivation of lysosomal acid alpha-glucosidase in the knockout mice does not contribute to the process of polyglucosan formation.

CONCLUSIONS

An imbalance between GSase and GBE activities is proposed as the mechanism involved in the production of polyglucosan bodies. The authors may have inadvertently created a "muscle polyglucosan disease" by simulating the mechanism for polyglucosan formation.

Novel missense mutations in the glycogen-branching enzyme gene in adult polyglucosan body disease

We describe the first non-Ashkenazi patient with adult polyglucosan body disease and decreased glycogen-branching enzyme (GBE) activity in leukocytes. Gene analysis revealed compound heterozygosity for two novel missense mutations Arg515His and Arg524Gln in the GBE gene. Both missense mutations are predicted to impair GBE activity. This is the first identification of GBE mutations underlying adult polyglucosan body disease in a non-Ashkenazi family, and confirms that adult glycogen storage disease type IV can manifest clinically as adult polyglucosan body disease.

[Glycogenosis type IV as a seldom cause of cardiomyopathy - report about a successful heart transplantation]

We report about a 17 year old male patient with a cardiomyopathy secondary to type IV glycogenosis (Andersens disease) and class II immunoglobulin deficiency who underwent cardiac transplantation. The patient first developed symptoms of heart failure at the age of twelve. The histologic diagnosis was cardiomyopathy secondary to glycogenosis. In addition, the patient suffered recurrent pulmonary infections and developed bronchiectases in the left lower lobe. This region was atelectatic since he was eleven. The patient did have two younger brothers who died of congestive heart failure at the age of nine and ten. Neither his parents nor anybody else of his relatives had a history of heart failure or glycogenosis. Since the patient suffered recurrent cardiac decompensations with the need for catecholamines he was accepted for cardiac transplantation although several relative contraindications to transplantation such as cachexia, myopathy, immunglobulin deficiency and bronchiectases had been present. The patient was transplanted successfully. The postoperative weaning from the respirator was markedly prolonged and complicated by pulmonary infection. Furthermore, mobilization was retarded. One year after transplantation, he is in a good condition without pulmonary or systemic infection. Right ventricular endomyocardial biopsies did not show recurrence of glycogenosis in the donor organ.

A novel missense mutation in the glycogen branching enzyme gene in a child with myopathy and hepatopathy

We have identified a novel missense mutation in the gene for glycogen branching enzyme (GBE 1) in a 16-month-old infant with a combination of hepatic and muscular features, an atypical clinical presentation of glycogenosis type IV (GSD IV). The patient was heterozygous for a G-to-A substitution at codon 524 (R524Q), changing an encoded arginine (CGA) to glutamine (CAA), while the GBE1 gene on the other allele was not expressed. This case broadens the spectrum of mutations in patients with GSD IV and confirms the clinical and molecular heterogeneity of this disease.

Early-onset fetal hydrops and muscle degeneration in siblings due to a novel variant of type IV glycogenosis

We report on 3 consecutive sib fetuses, presenting at 13, 12, and 13 weeks of gestation, respectively, with fetal hydrops, limb contractures, and akinesia. Autopsy of the first fetus showed subcutaneous fluid collections and severe degeneration of skeletal muscle. Histologic studies demonstrated massive accumulation of diastase-resistant periodic acid-Schiff-positive material in the skeletal muscle cells and epidermal keratinocytes of all 3 fetuses. Enzyme studies of fibroblasts from the 3rd fetus showed deficient activity of glycogen brancher enzyme, indicating that this is a new, severe form of glycogenosis type IV with onset in the early second trimester.

Prenatal diagnosis of glycogen storage disease type IV using PCR-based DNA mutation analysis

Deficiency of glycogen branching enzyme activity causes glycogen storage disease type IV (GSD-IV). Clinically, GSD-IV has variable clinical presentations ranging from a fatal neonatal neuromuscular disease, to a progressive liver cirrhosis form, and to a milder liver disease without progression. Current methods for prenatal and postnatal diagnosis are based on an indirect method of measuring the enzyme activity, which has a limited sensitivity and cannot be used to distinguish patients with these variable clinical phenotypes. In this study, a GSD-IV family with a non-progressive hepatic form of the disease requested prenatal diagnosis. Determination of the branching enzyme activity in cultivated amniocytes showed 20 per cent residual activity overlapping with the level detected in the heterozygotes. Mutation analysis revealed that the fetus carried two mutant alleles, L224P and Y329S, the same as the proband of this family. The fetus was predicted to be affected and postnatally his clinical presentation is consistent with the diagnosis. We conclude that DNA mutation analysis should be used in the prenatal diagnosis of GSD-IV, especially in the situation of high residual enzyme activity.